Multiple Trait Associations in Relation to Habitat Differentiation Among 17 Floridian Oak Species

Abstract

Differentiation of species distributions along environmental gradients and phenotypic specialization help explain the co-presence of 17 oak species that might otherwise be expected to competitively exclude one another. In an effort to understand the role of niche differentiation in the co-presence of these congeneric species in north-central Florida, we examined the community structure of oak-dominated forests in this region in relation to environmental variables and a suite of life history and physiological traits. Landscape distribution patterns of oaks and other woody species were determined from randomly established plots in three state parks. Soil moisture, nutrient availability, and fire regime were found to be critical factors influencing community structure, and the distribution of oak species was strongly correlated with these gradients. Detrended correspondence analysis of species' distributions supported the grouping of oak species into three major community types: (1) hammock, (2) sandhill, and (3) scrub. Principal components of multiple traits also supported differentiation of oak species into these three groups.There is clear evidence for ecological sorting among the oaks in these forests as species partition environmental gradients more than expected by chance, and most functional traits of species correspond to species distributions as predicted based on a priori understanding of trait function. Across phylogenetic lineages, species showed evolutionary convergence in function and habitat preference. In contrast, leaf-level traits were conserved within phylogenetic lineages and were not well correlated with local habitat factors, but rather with the broader geographic distributions and northern range limits of species. The cumulative results reported here provide strong evidence that oak species specialize for particular niches via trade-offs in functional traits, and such niche partitioning contributes to the high diversity of oak species at the landscape level. At smaller spatial scales, phylogenetic diversity among the oaks is likely to be important in promoting their coexistence through other mechanisms.

Trait-based community assembly of understory palms along a soil nutrient gradient in a lower montane tropical forest

“…Thus, resource-use strategies may influence community structure of understory palms in the lower montane forests of western Panama by promoting species turnover along soil nutrient gradients. (Wright et al 2002;Cavender-Bares et al 2004;Cornwell and Ackerly 2009), and soil nutrients (Paoli 2006;Ordonez et al 2009). In this study, we did not detect community-wide shifts in any trait with rainfall, suggesting that species sorting along rainfall gradients may be less important in regions with such high rainfall compared to those in lower rainfall regions.…”

“…Leaf N, leaf P, leaf 5 N, rachis length, SLA, A max(mass ), PNUE, and a multivariate combination of all measured traits increased, and leaf C:N decreased, with species distribution along a gradient of increasing soil nutrient availability. Leaf size and quality have also been found to increase with soil nutrient availability in other studies (Reich et al 2003;Cavender-Bares et al 2004;Ordonez et al 2009). Reciprocal transplant experiments comparing species performance in high and low nutrient soils have shown that differences in resourceuse efficiency (Baltzer et al 2005) and trade-offs between growth and herbivore defense (Cunningham et al 1999;Fine et al 2004) are important in maintaining soil-based habitat associations in other tropical forests.…”

“…Trait-based approaches have linked community structure and ecosystem function along various resource gradients (Reich et al 2003), particularly light (Poorter 1999;Poorter and Bongers 2006) and water (Wright et al 2001;Engelbrecht et al 2007;Sandel et al 2010) and to lesser extent soil nutrient (Wright et al 2001;Cavender-Bares et al 2004) gradients. Furthermore, the examination of leaf functional traits along resource gradients has led to hypotheses regarding plant strategies on local to global scales (Reich et al 2003;Lavorel and Gamier 2002) and to insights into processes generating community structure (Keddy 1992;Kraft et al 2008;Ackerly and Cornwell 2007).…”

“…Recent trait-based assessments of plant communities have identified two levels of niche processes influencing community structure: (1) 'habitat' or environmental filtering, whereby convergent trait values are expected for cooccurring species due to environmental trait selection, and (2) niche differentiation, whereby divergent trait values are expected due to interspecific competition among cooccurring species (Cavender-Bares et al 2004;Ackerly and Cornwell 2007;Kraft et al 2008). While these two niche processes represent opposing constraints on community structure, they can also act simultaneously (Weiher et al 1998;Kraft et al 2008;Cornwell and Ackerly 2010).…”

Plant functional traits and the multidimensional nature of species coexistence

“…For example, fitness and stabilizing niche differences could be correlated with distinct sets of traits (17). Moreover, it may be that niche and fitness differences are best described by multivariate suites of traits, supporting a hypothesis of high-dimensional coexistence between species in communities (18)(19)(20)(21).…”